1. Field of the Invention
The present invention relates to a phase adjustment device and a phase adjustment method for adjusting a phase (timing) of a pulse used when an image is obtained by a digital camera, and a digital camera in which the phase adjustment device is incorporated.
2. Description of the Related Art
In a digital camera, (digital still camera, digital video camera, mobile telephone provided with a camera, and the like), an analog imaging signal obtained by an imaging element such as CCD or a MOS sensor is converted into a digital imaging signal, and then, after being processed in a predetermined manner, the resultant is recorded. In order to obtain an image of a photographic subject using the imaging element, a pulse for detecting a signal level of the analog signal inputted from the imaging element, a pulse for driving the imaging element, and the like, are necessary, and it is difficult to adjust phases of these pulses in the hardware designing stage due to variability generated in the manufacturing process. Therefore, the phases are adjusted by a technician after the manufacturing process, and information showing the adjusted phases is stored in a memory region and read from the memory region when the product is actually used so that the phases are optimally set.
There is a known conventional technology wherein only a noise element is fetched in a minimum exposure time, and the phase is adjusted under such a condition that a high-frequency component (noise element) is minimized. An example of the technology is recited in No. 2005-151081 of the Japanese Patent Applications Laid-Open.
In the field of the digital camera, various changes may be made to a system where a phase adjustment device is incorporated. In the case where the digital camera is adopted as a medical-care camera, it is possible that the imaging element will be exchanged after the digital camera is manufactured. In the case where the system incorporating the phase adjustment device or the imaging element is thus subjected to some change, the phase of the pulse for detecting the signal level of the analog signal inputted from the imaging element also changes, which makes it necessary to readjust the phase. However, it is difficult to speedily and easily change the system incorporating the phase adjustment device or replace the imaging element when the technician has to manually readjust the phase.
Another disadvantage of the invention recited in the foregoing document is that, though there are various types of pulses to be adjusted, optimal phases of all of the pulses are calculated by means of the same method irrespective of characteristics of those pulses, resulting in failure to achieve a high accuracy in phase adjustment.
Further, in the digital camera, the phases of a plurality of horizontal transfer pulses in the imaging element (in particular, CCD) are generally adjusted by the technician in accordance with a mounting status. In the horizontal transfer pulses, the combination of a voltage of the first horizontal transfer pulse and a voltage of the second horizontal transfer pulse are controlled, and the depths of potential wells are thereby controlled so that signal charges are transferred. The control is thus made as a countermeasure against shadings which are generated on right and left sides of a screen due to the deterioration of an efficiency level in the transfer when the phases of the horizontal transfer pulses are inappropriate. The shadings are the unevenness generated on the screen. An amount of the charges decreases in a pixel having a larger number of transfer stages in the horizontal transfer CCD, and the shadings are thereby generated due to the different charge amounts on the right and left sides of the screen. As a result, an image quality is deteriorated.
However, in the conventional manner wherein the technician manually adjusts the phases of the horizontal transfer pulses in a manner similar to the other pulses, it is difficult to change the system incorporating the phase adjustment device and exchange the imaging element in a speedy and easy manner.